1. Field of the Invention
This invention relates to electronic circuits that are formed by printing on a substrate, and more particularly, to a method of fabricating electronic circuits having active and passive components on any substrate by adhering to a seed layer that has been printed on the substrate.
2. Description of the Related Art
Substrates having electrically conductive lines thereon are used in a wide variety of electronic applications. Glass substrates used for LCD's, touch screens for visual displays, consumer electronic displays, from cell phone to portable computers all require electrically conductive lines to be formed thereon to provide the desired functionality. Flexible substrates are also used in a wide variety of applications, such as for the coupling of electronic components in a system or the transfer of data. Flexible substrates may be made of a polyimide film, such as Kapton, or from thin plastic or metal materials.
Epoxy resin is commonly used to laminate fiberglass layers to provide a substrate in various electronic components and computer systems. For example, the motherboard of the computer to which the CPU is coupled and electrically connected to other components on the motherboard is typically made from an epoxy resin laminate that includes one or more fiberglass layers. Memory boards, keypad support substrates, the interior electronic support boards of calculators, cell phones, flash disk drives and numerous other electronic components are typically mounted on such fiberglass epoxy laminate substrates.
The processing of such circuits requires numerous high temperature steps. The high temperature may not be compatible with other circuit components to be formed on the substrate.
Forming electrically conductive lines on various substrates presents particular technical challenges for each substrate. The techniques for forming the conductive lines and electronic circuits must be adapted to each particular substrate which often requires an initial investment, and technical changes or technology advancement. For example, placing an conductive circuit on glass, quartz and other rigid substrates requires very different equipment and handling techniques than can be used with fiberglass epoxy laminate, which are not as rigid. Similarly, forming electronic circuits on flexible substrates requires completely different machinery and equipment than can be used with glass or an epoxy laminate substrate.
An additional technical difficulty is the selection of different materials which can be formed on a particular substrate and the cost associated with using different materials for different substrates. For example, on some substrates aluminum can easily be formed as an electrical interconnection circuit. However, aluminum has a higher resistivity than other conductors, such as copper and gold. In addition, aluminum is not as suitable for forming certain electronic components such as capacitors and inductors as other metals and materials. It is therefore desired, in some substrates to provide electronic circuits having different types of metal for different functions, for example using copper and aluminum for certain electrical connection lines while using other materials such as metal oxides, dielectrics or magnetic metals for such components as resistors, capacitors and inductors, respectively. Yet the high-temperature steps, and etch chemistry for one material is often not compatible with other materials.
For example, many of these alternative elements are not compatible with the etch processes which are traditionally used for forming aluminum. Therefore, considerable expense is added to a simple electronic circuit if different materials are used. This requires substantial masking and etching followed by the appropriate clean and preparation steps for each different type of material.
For many types of materials it is common to deposit the entire material in a uniform film across the entire substrate. After the film is deposited, the layer is patterned by masking then developed and etched, each of which require movement of the substrate to different machines and some of which require complex chemistry which may affect other circuits or components if they have been previously formed on the substrate. This requires that protective layers be provided to cover previously formed layers while the deposition and etching is carried out on later prepared layers even though such layers may be electrically connected to each other.
Adding to the difficulty and expense is the need to manufacture different masks for each of the patterns to be etched in many of the processes today. For many electrical circuits formed on substrates today, once a pattern is determined, a mask must be formed which corresponds to the desired pattern. After the mask is formed, many circuits can be constructed with the same mask. If a change to the circuit is required, even of a very minor nature, a completely new mask is required with the attendant time and expense to obtain and implement such a mask before a layer in the new pattern can be formed on the substrate. Accordingly, the forming of custom electrical circuits on any given substrate is extremely expensive in the technology of today. The expense is amplified if a low number of the circuits are built, thus drastically increasing the cost per circuit.